Metal nano particle and method for manufacturing them and conductive ink

ABSTRACT

A method of producing hydrophobic metal nanoparticles using a hydrophobic solvent, having uniform particle size distribution and high yield rate to allow mass production; the metal nanoparticles thus produced; and conductive ink including the metal nanoparticles are disclosed. According to one aspect of the invention, a method of producing metal nanoparticles is provided, comprising dissociating a metal compound with an amine-based compound, and adding a hydrocarbon-based compound and either one of an alkanoic acid or a thiol-based compound to the dissociated metal ion solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2005-39013 filed on May 10, 2005 and Korean Patent Application No.2005-55186 filed on Jun. 24, 2005, the contents of which areincorporated here by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a method of producing metalnanoparticles and the metal nanoparticles thus produced, and inparticular, to a method of producing metal nanoparticles by the solutionmethod.

2. Description of the Related Art

There are two major methods of producing metal nanoparticles, namely thevapor method and the solution method (colloid method). However, sincethe vapor method which uses plasma or gas evaporation requires highlyexpensive equipment, the solution method is generally used, which ismore easily utilized in mass production.

One existing method of producing metal nanoparticles by the solutionmethod is to dissociate a metal compound in a hydrophilic solvent andapply reducing agents or surfactants to produce the metal nanoparticlesin the form of a hydrosol. Another method is the phase transfer method,which involves moving the compound from a hydrophilic solvent to ahydrophobic solvent to form metal nanoparticles that may be dispersed ina hydrophobic solvent. However, the production of metal nanoparticles bysuch existing methods provides a very low yield rate, as it is limitedby the concentration of the metal compound solution. That is, it ispossible to form metal nanop articles of uniform size only when theconcentration of the metal compound is less than or equal to 0.01M.Thus, there is a limit also on the yield of metal nanoparticles, and toobtain metal nanoparticles of uniform size in quantities of severalgrams, 1000 liters or more of functional group are need. This presents alimitation to efficient mass production. Moreover, the phase transfermethod necessarily requires a phase transfer, which is a cause ofincreased production costs.

Further, the production of metal nanoparticles having alkanoates ascapping molecules using existing methods entails a complicated process,as it includes at least two or more steps. For example, the existingproduction method of silver nanoparticles must proceed through a step ofadding NaOH in an alkanoic acid solution to synthesize Na-alkanoate, astep of reacting the Na-alkanoate with silver salt dissociated in waterto form Ag-alkanoate powder, and a step of dissolving the Ag-alkanoatepowder in an organic solvent for heating, to obtain silvernanoparticles. The several steps thus needed for the production of metalnanoparticles can be a waste of time and effort.

SUMMARY

The present invention provides a method of producing metal nanoparticlesusing a hydrophobic solvent, having uniform particle size distributionand high yield rate to allow mass production. Also, the presentinvention provides metal nanoparticles having alkanoate molecules orsulfur molecules, produced at a low cost by an integrated procedure, andprovides conductive ink including the metal nanoparticles thus obtained.

Additional aspects and advantages of the present invention will be setforth in part in the description which follows and, in part, will beobvious from the description, or may be learned by practice of theinvention.

One aspect of the invention may provide a method of producing metalnanoparticles, comprising dissociating a metal compound with anamine-based compound, and adding a hydrocarbon-based compound and eitherone of an alkanoic acid or a thiol-based compound to the dissociatedmetal ion solution.

Here, the metal compound may include one or more metals selected from agroup consisting of silver (Ag), copper (Cu), nickel (Ni), gold (Au),platinum (Pt), palladium (Pd), and iron (Fe). In a preferred embodiment,the metal compound may include one or more compounds selected from agroup consisting of AgNO₃, AgBF₄, AgPF₆, Ag₂O, CH₃COOAg, AgCF₃SO₃, andAgClO₄.

Also, the amine-based compound may have a composition ofC_(x)H_(2x+1)NH₂, where x may be an integer from 2 to 20. In a preferredembodiment, the amine-based compound may be one or more compoundsselected from a group consisting of butylamine, propylamine, octylamine,decylamine, dodecylamine, hexadecylamine, and oleylamine. Further, themole ratio of the amine-based compound to the metal compound may rangefrom 1 to 100.

In addition, the hydrocarbon-based compound may be one or more compoundsselected from a group consisting of hexane, octane, decane, tetradecane,hexadecane, 1-hexadecene, 1-octadecene, toluene, xylene, andchlorobenzoic acid. Here, the hydrocarbon-based compound may be added sothat the concentration of the metal compound becomes a mole ratio of0.001 to 10.

The alkanoic acid may have a composition of RCOOH, where R may be asaturated or unsaturated aliphatic hydrocarbon from C1 to C20. In apreferred embodiment, the alkanoic acid may be one or more acidsselected from a group consisting of lauric acid, oleic acid, decanoicacid, and palmitic acid. Also, the mole ratio of the alkanoic acid tothe metal compound may range from 0.1 to 1.

The thiol-based compound may have a composition of C_(y)H_(2y+1)SH,where y may be an integer from 2 to 20. In a preferred embodiment, thethiol-based compound may be one or compounds selected from a groupconsisting of linear-structure octanethiol, decanethiol, dodecanethiol,tetradecanethiol, hexadecanethiol, octadecanethiol andbranched-structure 2-methyl-2-propanethiol. Also, the mole ratio of thethiol-based compound to the metal compound may range from 0.1 to 1.

In addition, a reducing agent may further be added during the adding ofa hydrocarbon-based compound and either one of an alkanoic acid or athiol-based compound to the dissociated metal ion solution. Here, thereducing agent may be one or more compounds selected from a groupconsisting of boron hydroxide, hydrazine, alcohol, amide, acid, andglucose. In a preferred embodiment, the reducing agent may be one ormore compounds selected from a group consisting of NaBH4, LiBH4,tetrabutylammonium borohydride, N2H4, glycol, glycerol,dimethylformamide, tannic acid, citrate, and glucose. Also, the moleratio of the reducing agent to the metal compound may range from 0.1 to1.

Another aspect of the invention may provide metal nanoparticles producedby a method comprising dissociating a metal compound with an amine-basedcompound, and adding a hydrocarbon-based compound and an alkanoic acidto the dissociated metal ion solution.

Here, the size of the metal nanoparticles may be 1 to 40 nm, and themetal nanoparticles may include 10 to 40 weight % organic componentsamong the metal nanoparticles. Further, the metal nanoparticles may beused an antibiotic, a deodorant, a disinfectant, a conductive adhesive,a conductive ink, or an electromagnetic shield coating for a displaydevice.

Still another aspect of the invention may provide metal nanoparticlesproduced by a method comprising dissociating a metal compound with anamine-based compound, and adding a hydrocarbon-based compound and athiol-based compound to the dissociated metal ion solution.

Here, the size of the metal nanoparticles may be 1 to 20 nm, and themetal nanoparticles may have 1 to 6 weight % of sulfur. The metalnanoparticles may be used an antibiotic, a deodorant, a disinfectant, aconductive adhesive, a conductive ink, or an electromagnetic shield fora display device.

Yet another aspect of the invention may provide conductive ink includingmetal nanoparticles produced by a method comprising dissociating a metalcompound with an amine-based compound, and adding a hydrocarbon-basedcompound and either one of an alkanoic acid or a thiol-based compound tothe dissociated metal ion solution.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present invention willbecome apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a graph representing the results of UV-VIS spectroscopy formetal nanoparticles produced according to an embodiment of theinvention;

FIG. 2 is a TEM (transmission electron microscope) image of metalnanoparticles produced according to an embodiment of the invention;

FIGS. 3 to 5 are graphs representing the results of TGA(thermo-gravimetric analysis) for metal nanoparticles produced accordingto embodiments of the invention;

FIG. 6 is a graph representing the results of UV-VIS spectroscopy formetal nanoparticles produced according to an embodiment of theinvention;

FIG. 7 is a TEM image of metal nanoparticles produced according to anembodiment of the invention;

FIG. 8 is a graph representing the results of TGA (thermo-gravimetricanalysis) for metal nanoparticles produced according to an embodiment ofthe invention; and

FIG. 9 is a graph representing the results of WAXS (wide-angle X-rayscattering) analysis of silver thiolate for producing metalnanoparticles according to an embodiment of the invention.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments will be described in detail of themethod of producing metal nanoparticles and the metal nanoparticles thusproduced according to the present invention.

Any precursor including metals, as generally used in the production ofmetal nanoparticles, may be used as the metal compound in the presentinvention, preferably that which is dissociated well in a hydrophobicsolvent. Here, examples of such a metal compound include at least onemetal selected from a group consisting of silver, copper, nickel, gold,platinum, palladium, iron, or an alloy thereof. Specific examples mayinclude inorganic acid salts, such as nitrates, carbonates, chlorides,phosphates, borates, oxides, sulfonates, and sulfates, etc., and organicacid salts, such as stearate, myristate, and acetate, etc. The use ofnitrates may be more preferable, as they are economical and widely used.More specific examples for the metal compound may include silvercompound solutions, such as of AgNO₃, AgBF₄, AgPF₆, Ag₂O, CH₃COOAg,AgCF₃SO₃, and AgClO₄, copper compound solutions, such as of Cu(NO₃),CuCl₂, and CuSO₄, and nickel compound solutions, such as of NiCl₂,Ni(NO₃)₂, and NiSO₄, etc.

Although these metal compounds are generally known to dissociate well ina hydrophilic solvent, the present invention presents a method by whichthe metal compound is dissociated in a hydrophobic solvent. Anamine-based compound was selected as this hydrophobic solvent. Thus,when a hydrocarbon-based compound was added later as a reflux solvent,the solubility is increased between the metal ion solution dissociatedby the amine-based compound and the hydrocarbon-based compound.Therefore, the metal nanoparticles may consequently be retrieved with ahigh yield rate.

The amine-based compound may have a composition of C_(x)H_(2x+1)NH₂,where x is an integer between 2 to 20. To dissociate the metal compound,it may be preferable for the amine-based compound to be in a liquidstate. Examples of such an amine-based compound include propylamine(C₃H₇NH₂), butylaamine (C₄H₉NH₂), octylamine (C₈H₁₇NH₂), decylaamine(C₁₀H₂₁NH₂), dodecylamine (C₁₂H₂₅NH₂), hexadecylamine (C₁₆H₃₃NH₂), andoleylamine (C₁₈H₃₅NH₂), preferably butylamine and propylamine, and morepreferably propylamine, because butylamine and propylamine have superiorcharacteristics of dissociating metal compounds, where propylamine has agreater ability of dissociating silver salts than does butylamine.Although octylamine and oleylamine are also liquids, their abilities todissociate silver salts are inferior compared to that of butylamine orpropylamine. Among the above amine-based compounds, decylamine(C₁₀H₂₁NH₂). dodecylamine (C₁₂H₂₅NH₂), and hexadecylamine (C₁₆H₃₃NH₂)are solid, and may be used by applying heat or dissolving in an organicsolvent.

In a preferred embodiment, the amine-based compound may be mixed withthe metal compound in a mole ratio of 1 or greater. For the amine-basedcompounds of propylamine and butylamine, a mole ratio of 1 to 100 ispreferable, considering the reaction conditions and yield rate, etc.Thus, the amine-based compound may be mixed in a mole ratio of 1 to 100with respect to the metal compound, where it may be preferable in termsof economy to mix as little as possible, within a range where the metalcompound can be dissociated.

The reflux solvent and capping molecules are added to the metal ionsolution dissociated via the process set forth above.

A variety of organic solvents may be selected for the reflux solventadded to adjust the reflux temperature. Since an amine-based compound,which is a hydrophobic solvent, is used as the dissociation solvent inthe present invention, it is preferable that a hydrophobic organicsolvent be used also for the reflux solvent. A representativehydrophobic solvent is the hydrocarbon-based compound. Thus, the type ofhydrocarbon-based compound is selected based on the desired refluxconditions. Preferred examples of a hydrocarbon-based compound includehexane, octane, decane, tetradecane, hexadecane, 1-hexadecene,1-octadecene, toluene, xylene, and chlorobenzoic acid, etc. For thereflux solvent, toluene, xylene, 1-hexadecene, chlorobenzoic acid, or1-octadecene is more preferable. This is because it is preferable forthe mixed solution to be refluxed at a temperature of 100° C. or aboveto produce the desired forms of metal nanoparticles of the presentinvention, and the boiling point is 110.6° C. for toluene, 140° C. forxylene, 274° C. for 1-hexadecene, 320° C. for 1-octadecene, and 190° C.for chlorobenzoic acid, to be in correspondence with such temperaturecondition. The reflux solvents listed as examples set forth above arepreferable also in terms of economy. The reflux temperatures areselected to range from 100 to 400° C.

It may be preferable that the hydrocarbon-based compound, such asdescribed above, be added to the dissociated metal ion solution so thatthe concentration of the metal compound ranges from 0.001 to 10 moleratio, since the reflux conditions may be formed within this range ofmole ratio that are suitable for obtaining metal nanoparticles. Thehigher concentration of the metal compound, the smaller size of thefunctional group, to be preferable in terms of economy as massproduction is made possible. The concentration of the metal compound isultimately related to the yield rate of the metal nanoparticles, and inthe existing solution method, the metal nanoparticles are formed only ata low concentration of 0.01 mole ratio or less, to result in a low yieldrate. Using the present invention, however, the metal nanoparticles maybe formed at a high concentration to ensure a high yield rate.

In the solution method, capping molecules are required to produce metalnanoparticles, where compounds having oxygen, nitrogen, and sulfur atomsmay be used as such capping molecules. More specifically, compounds ofthe thiol group (—SH), amine group (—NH₂), or carboxyl group (—COOH) maybe used, and in the present invention, compounds having alkanoatemolecules (—COOR) or thiol-based compounds are used as the cappingmolecules.

According to an embodiment of the invention, the alkanoate moleculeswhen used as capping molecules mix readily with hydrophobic solvents,and bond with metal nanoparticles by a certain strength to form metalnanoparticles that are stable. Also, when metal nanoparticles havingalkanoate molecules are used as conductive ink, the capping moleculesmay be removed easily by firing, to form wiring that is superior inelectrical conductivity.

In the present invention, alkanoic acid is used as the compound havingalkanoate molecules. Alkanoic acid has a composition of RCOOH, where Ris a saturated or unsaturated aliphatic hydrocarbon from C₁ to C₂₀. Thatis, R may be an alkyl group from C₁ to C₂₀, an alkenyl group from C₁ toC₂₀, or an alkylene group from C₁ to C₂₀.

Examples of such an alkanoic acid include lauric acid (C₁₁H₂₃COOH),oleic acid (C₁₇H₃₃COOH), decanoic acid (C₉H₁₉COOH), and palmitic acid(C₁₅H₃₁COOH), etc. In a preferred embodiment of the invention, lauricacid and oleic acid are used for their advantages in terms of yield rateand conductivity.

Preferably, the alkanoic acid is added in a mole ratio of 1 or lowerwith respect to the metal compound, since the addition in a higher ratiowill result in left-over alkanoic acid after a 1:1 reaction with themetal compound to produce side reactions, or incur a waste of thealkanoic acid. Thus, adding the alkanoic acid in a mole ratio of 1 withrespect to the metal compound is preferable in terms of economy. Inaddition, for capping the metal nanoparticles, the alkanoic acid must beadded in a mole ratio of 0.1 or higher with respect to the metalcompound.

Compared to the existing method of producing metal nanoparticles havingalkanoate molecules, it is not necessary to proceed through the step offorming alkanoate compounds of alkali metals in the present invention,and the metal nanoparticles may be produced in an integrated procedure,so that the production process may be simplified and the productioncosts reduced.

According to another embodiment of the invention, a thiol-based compoundis used as the capping molecules. The thiol-based compound has acomposition of C_(y)H_(2y+1)SH, where y may be selected from 2 to 20.Preferred examples of a thiol-based compound include linear-structureoctanethiol (C₈H₁₇SH), decanethiol (C₁₀H₂₁SH), dodecanethiol (C₁₂H₂₅SH),tetradecanethiol (C₁₄H₂₉SH), hexadecanethiol (C₁₆H₃₃SH), octadecanethiol(C₁₈H₃₇SH) and branched-structure 2-methyl-2-propanethiol (C₄H₉SH). In apreferred embodiment of the invention, dodecanethiol (C₁₂H₂₅SH) or2-methyl-2-propanethiol (C₄H₉SH) is used as the thiol-based compound.Preferably, the thiol-based compound is added in a mole ratio of 1 orlower with respect to the metal compound, since the addition of thethiol-based compound in a higher ratio makes it difficult for the metalnanoparticles to be created. More preferably, a mole ratio of 0.5 isused. Also, for capping the metal nanoparticles, the thiol-basedcompound must be added in a mole ratio of at least 0.1.

To use a hydrocarbon-based compound having a boiling point of 50° C. ormore as the reflux solvent in the present invention, or in order toincrease the yield rate of the metal nanoparticles produced, thereducing agent may be added further. Examples of such reducing agentinclude borate hydroxide, hydrazine, alcohol, amide, acid, and glucose,etc. More specific examples may include borate hydroxides such as NaBH4,LiBH4, and tetrabutylammonium borohydride (TBAB), hydrazines such asN2H4, alcohol such as glycol and glycerol, amides such asdimethylformamide (DMF), acids such as tannic acid and citrate, andglucose. In general, TBAB is preferable for a reducing agent used in ahydrophobic solvent.

When a reducing agent is added, rapid exothermic reactions may occur, aswell as rapid fusion and growth of the particles. It may thus bedifficult to control the metal particles, and side reactions may occur,so that care is needed in using a reducing agent.

Preferably, the reducing agent should be added in a mole ratio of 1 orlower with respect to the metal compound, since the addition of areducing agent in a higher mole ratio causes fusion between the metalparticles to decrease the yield rate of nano-sized metal particles, andmay also cause an explosion due to rapid exothermic reactions. Also, inorder for the reducing agent to function as a reducing agent, it must beadded in a mole ratio of 0.1 or higher. Therefore, it is preferable thatthe reducing agent be added in a mole ratio of 0.1 to 1 with respect tothe metal compound.

In a preferred embodiment of the invention, a hydrocarbon-based compoundand an alkanoic acid are added to the metal ion solution dissociatedwith an amine-based compound as described above, and the mixed solutionis refluxed, where a reducing agent may optionally be added further. Thereflux temperature is determined according to the boiling point of theselected hydrocarbon-based compound. The reflux starts at 18° C. with atemperature range of 100° C. to 400° C., and proceeds for 1 to 24 hours.Preferably, the metal nanoparticles will be obtained after 2 to 4 hoursat 100° C.

At the initial stage of the reflux reaction, the mixed solution is awhite slurry, turning more and more yellow, and as the reactionprogresses, transforms from a transparent yellow to a red, and then abrown color. Whether or not the metal nanoparticles have formed may bedetermined by this change in color. The metal nanoparticles thus formedmay be retrieved without a sorting process, by precipitating in a polarsolvent and performing centrifugal separation. This is because theformed metal nanoparticles are uniform in size, to render the sortingprocess unnecessary. The polar solvent may include acetone, ethanol,methanol, or a mixed solution thereof.

The metal nanoparticles thus retrieved have a size of 1 to 40 nm, andpreferably, metal nanoparticles were obtained that had a uniform size of5 to 10 nm. FIG. 1 is a graph representing the results of UV-VISspectroscopy for metal nanoparticles produced according to a preferredembodiment of the invention. Referring to FIG. 1, a graph is shown forthe analysis results of silver nanoparticles obtained by a productionmethod according to the present invention, having a maximum lightabsorbance in the wavelength region of 420 nm. Considering the fact thatthe maximum light absorbance is shown in the wavelength region of 380 to240 nm for silver particulates of several or several tens of nm, it isseen that the graph of FIG. 1 shows a typical silver plasmon peak. FIG.2 is a TEM (transmission electron microscope) image of the metalnanoparticles produced according to a preferred embodiment of theinvention. Referring to FIG. 2, the analysis results of the silvernanoparticles obtained by a production method according to the presentinvention show that silver nanoparticles are formed that have a uniformsize of 7 nm. The image further shows that the silver nanoparticlesobtained are superior also in terms of dispersion stability.

Also, among the metal nanoparticles obtained using alkanoates as cappingmolecules, organic components occupy 10 to 40 weight %. FIGS. 3 to 5 aregraphs representing the results of TGA (thermo-gravimetric analysis) formetal nanoparticles produced according to preferred embodiments of theinvention. Referring to FIG. 3, the results of thermo-gravimetricanalysis on silver nanoparticles obtained by a production methodaccording to the present invention and capped with decanoic acid show aweight reduction of about 17 weight % at a high temperature of 300° C.or more. Also, referring to FIG. 4, the results of thermo-gravimetricanalysis on silver nanoparticles obtained by a production methodaccording to the present invention and capped with lauric acid show aweight reduction of about 25 weight %, and referring to FIG. 5, theresults of thermo-gravimetric analysis on silver nanoparticles obtainedby a production method according to the present invention and cappedwith oleic acid show a weight reduction of about 33 weight %. Thus, itis seen that among the silver nanoparticles obtained by a productionmethod according to the present invention, the weight occupied byorganic components is 10 to 40 weight %, preferably 15 to 35 weight %.Among the organic components in FIGS. 3 to 5 respectively, the oxygencontent was 3 to 4 weight %. In an embodiment of the present invention,the oxygen content among the organic components is 1 to 6 weight %,preferably 2 to 5 weight %.

In another preferred embodiment of the invention, a hydrocarbon-basedcompound and a thiol-based compound are added to the metal ion solutiondissociated with an amine-based compound as described above, and themixed solution, in which a reducing agent may optionally be added, isrefluxed according to the boiling point of the added hydrocarbon-basedcompound. This reflux is performed at 18 to 200° C. for 1 to 24 hours,preferably at 130° C. or more for 2 to 4 hours.

At the initial stage of the reflux reaction, the mixed solution is awhite slurry, turning more and more yellow, and as the reactionprogresses, transforms from a transparent yellow to a red, and then abrown color. Whether or not the metal nanoparticles have formed may bedetermined by this change in color. The metal nanoparticles thus formedmay be retrieved without a sorting process, by precipitating in a polarsolvent and performing centrifugal separation. This is because theformed metal nanoparticles are uniform in size, to render the sortingprocess unnecessary. Examples of the polar solvent may include acetone,ethanol, methanol, or a mixed solution thereof, etc.

The metal nanoparticles thus retrieved have a size of 1 to 50 nm, andpreferably, metal nanoparticles were obtained that had a uniform size of3 to 20 nm. Moreover, the metal nanoparticles are produced in ahigh-viscosity hydrophobic hydrocarbon-based compound, for a superioryield rate of 10 to 20 %. Also, since thiol is used for the cappingmolecules, the metal nanoparticles obtained have a 1 to 5 weight % ofsulfur (S).

FIG. 6 is a graph representing the results of UV-VIS spectroscopy formetal nanoparticles produced according to an embodiment of theinvention. Referring to FIG. 6, the graph shows a maximum lightabsorbance in the wavelength region of 420 nm. Considering the fact thatthe peak occurs in the wavelength region of 380 to 240 nm for silverparticulates of several or several tens of nm, it is seen that the graphof FIG. 4 shows a typical silver plasmon peak.

FIG. 7 is a TEM image of metal nanoparticles produced according to anembodiment of the invention. Referring to FIG. 7, it is seen that silvernanoparticles are formed that have a uniform size of 5 nm. It is alsoseen that the dispersion stability is highly superior.

FIG. 8 is a graph representing the results of TGA for metalnanoparticles produced according to an embodiment of the invention.Referring to FIG. 8, the results of thermo-gravimetric analysis onsilver nanoparticles obtained by a production method according to thepresent invention and capped with dodecanethiol show a weight reductionof about 19 weight % at a high temperature of 300° C. or more. Thus, itis seen that among the silver nanoparticles obtained by a productionmethod according to the present invention, the weight occupied byorganic components is 10 to 40 weight %. Among the organic components,the content of sulfur was about 3 weight %. In an embodiment of thepresent invention, the oxygen content among the organic components is 1to 6 weight %, preferably 2 to 5 weight %.

The yield rate may also be increased to 40% or higher, for metalnanoparticles produced in a high-viscosity hydrophobic hydrocarbon-basedcompound as in the present invention. This would be a benefit of fourtimes the efficiency, when compared with existing production methodswhich provide yield rates of about 10% only. Until now, the maximumamount of metal nanoparticles obtainable in a single process, whenproducing metal nanoparticles in a laboratory scale was known to beabout 40 g. Using a production method of the present invention, however,more than 100 g of metal nanoparticles may be obtained.

The metal nanoparticles thus obtained may be used as desired as anantibiotic, a deodorant, a disinfectant, conductive adhesive, conductiveink, or an electromagnetic shield for a display device. When the metalnanoparticles are used as conductive ink, the metal nanoparticles may bedispersed in a hydrophobic hydrocarbon-based solvent. This is becausethe solubility of the metal nanoparticles is high in hydrocarbon-basedsolvents, since they are produced in a hydrophobic solvent.

Embodiments relating methods of producing metal nanoparticles were setforth above, and hereinafter, explanations will be given in greaterdetail with reference to specific examples.

EXAMPLE 1

5 g of AgNO₃ was dissociated in 20 g of butylamine. The color of thesolution was transparent. Here, 50 ml of toluene and 5.6 g of lauricacid were added. This mixed solution was heated to 110° C., which is theboiling point of toluene. After refluxing for 4 hours, the solutionturned into a red color, and ultimately into a thick brown color. Amixture of acetone, ethanol, and methanol was added to the thick brownsolution, to precipitate silver nanoparticles. These precipitates werecollected after centrifugal separation. Analyzing these precipitateswith a UV-VIS spectroscope provided a graph having a peak such as thatin FIG. 1, by which it was found that 0.3 g of silver nanoparticleshaving sizes of 1 to 40 nm were obtained. From the results of TEManalysis on the particles after centrifugal separation, it was foundthat particles having a uniform size of 7 nm were obtained, as in FIG.2.

EXAMPLE 2

5 g of AgNO₃ was dissociated in 20 g of butylamine. The color of thesolution was transparent. Here, 50 ml of toluene and 5.6 g of lauricacid were added. Here, 1.6 g of TBAB was added further, which is areducing agent. With the addition of TBAB, the color of the solutionturned red. As the solution was heated up to 110° C., the boiling pointof toluene, and refluxed for 2 hours, the solution gradually turned intoa thick brown color. A mixture of acetone, ethanol, and methanol wasadded to the thick brown solution, to precipitate silver nanoparticles.After centrifugal separation of the precipitates, 1.2 g of silvernanoparticles were obtained. From the results of TEM analysis on theparticles, it was found that particles having a uniform size of 7 nmwere formed.

EXAMPLE 3

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. Here, 100 g of xylene was added and themixture stirred. Here, 20 g of lauric acid was further added, and thesolution was refluxed for 20 minutes while being heated up to 140° C.,the boiling point of xylene. As the reaction progressed, the solutionturned into a red color, and ultimately into a thick brown color. Amixture of acetone, ethanol, and methanol was added to the thick brownsolution, to precipitate silver nanoparticles. After centrifugalseparation of the precipitates, 1.6 g of silver nanoparticles wereobtained. From the results of TEM analysis on the particles, it wasfound that particles having a uniform size of 6 nm were formed.

EXAMPLE 4

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. The mixture was stirred after adding 100 gof xylene. Here, 20 g of oleic acid was further added, and the solutionwas refluxed for 20 minutes while being heated up to 140° C., theboiling point of xylene. As the reaction progressed, the solution turnedinto a red color, and ultimately into a thick brown color. A mixture ofacetone, ethanol, and methanol was added to the thick brown solution, toprecipitate silver nanoparticles. After centrifugal separation of theprecipitates, 3 g of silver nanoparticles were obtained. From theresults of TEM analysis on the particles, it was found that particleshaving a uniform size of 7 nm were formed.

EXAMPLE 5

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. The mixture was stirred after adding 100 gof xylene. Here, 20 g of lauric acid was added, and 3.2 g of TBAB, whichis a reducing agent, was added further. With the addition of TBAB, thecolor of the solution turned dark red. The solution was refluxed for 90minutes while being heated up to 140° C., the boiling point of xylene.The solution turned into a thick brown color. A mixture of acetone,ethanol, and methanol was added to the thick brown solution, toprecipitate silver nanoparticles. After centrifugal separation of theprecipitates, 5 g of silver nanoparticles were obtained. From theresults of TEM analysis on the particles, it was found that particleshaving a uniform size of 7 nm were formed.

EXAMPLE 6

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. The mixture was stirred after adding 100 gof xylene. Here, 20 g of oleic acid was added, and 3.2 g of TBAB, whichis a reducing agent, was added further. With the addition of TBAB, thecolor of the solution turned dark red. The solution was refluxed for 90minutes while being heated up to 140° C., the boiling point of xylene.The solution turned into a thick brown color. A mixture of acetone,ethanol, and methanol was added to the thick brown solution, toprecipitate silver nanoparticles. After centrifugal separation of theprecipitates, 6 g of silver nanoparticles were obtained. From theresults of TEM analysis on the particles, it was found that particleshaving a uniform size of 7 nm were formed.

EXAMPLE 7

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. The mixture was stirred after adding 100 gof hexane. Here, 20 g of lauric acid was added, and 3.2 g of TBAB, whichis a reducing agent, was added further. With the addition of TBAB, thecolor of the solution turned dark red. As the solution was refluxed for2 hours while being heated up to 69° C., the boiling point of hexane,the solution turned into a thick brown color. A mixture of acetone,ethanol, and methanol was added to the thick brown solution, toprecipitate silver nanoparticles. After centrifugal separation of theprecipitates, 0.8 g of silver nanoparticles were obtained. From theresults of TEM analysis on the particles, it was found that particleshaving a uniform size of 7 nm were formed.

EXAMPLE 8

16 g of AgNO₃ was dissociated in 30 g of butylamine. The color of thesolution was a faint yellow. The mixture was stirred after adding 100 gof hexane. Here, 20 g of oleic acid was added, and 3.2 g of TBAB, whichis a reducing agent, was added further. With the addition of TBAB, thecolor of the solution turned dark red. As the solution was refluxed for2 hours while being heated up to 69° C., the boiling point of hexane,the solution turned into a thick brown color. A mixture of acetone,ethanol, and methanol was added to the thick brown solution, toprecipitate silver nanoparticles. After centrifugal separation of theprecipitates, 1.2 g of silver nanoparticles were obtained. From theresults of TEM analysis on the particles, it was found that particleshaving a uniform size of 7 nm were formed.

COMPARISON 1

10 g of NaOH was added to 50 g of an aqueous lauric acid solution tosynthesize Na-dodecanoate of C₁₁H₂₃COO⁻Na⁺. 22 g of this Na-dodecanoatewas mixed with 16 g of an aqueous AgNO₃ solution for a cation exchangereaction to obtain Ag-dodecanoate in the form of a white powder. When 6g of Ag-dodecanoate is mixed with 100 g of a 1-octadecene solvent atnormal temperature, the mixed solution was untransparent. As thetemperature was increased to 120° C. and higher, the Ag-dodecanoate isdissolved to form a transparent solution, and as the temperature wasincreased to 150° C. and higher, the solution turned into a faint redcolor and ultimately into a dark red color. Here, an organic solvent wasadded and silver nanoparticles precipitated, after which 0.2 g of metalnanoparticles were retrieved by centrifugal separation.

COMPARISON 2

13 g of KOH was added to 70 g of an aqueous oleic acid solution tosynthesize K-oleate of C₁₇H₃₃COO⁻K⁺. 39 g of this K-oleate was mixedwith 16 g of an aqueous AgNO₃ solution for a cation exchange reaction toobtain Ag-oleate in the form of a white powder. When 8 g of Ag-oleate ismixed with 100 g of a 1-octadecene solvent at normal temperature, themixed solution was untransparent. As the temperature was increased to150° C. and higher, the Ag-dodecanoate is dissolved to form atransparent solution, and as the temperature was increased to 200° C.and higher, the solution turned into a faint red color and ultimatelyinto a dark red color. Here, a polar solvent was added and silvernanoparticles precipitated, after which 0.8 g of metal nanoparticleswere retrieved by centrifugal separation.

Production of Conductive Ink

100 g of silver nanoparticles 6 to 7 nm in size, produced by Examples 1through 8, were placed in an aqueous diethylene glycol butyl etheracetate and ethanol solution, and dispersed with an ultra-sonicator toproduce 20 cps of conductive ink. The conductive ink thus produced maybe printed on a circuit board via inkjet techniques to form conductivewiring.

According to the Comparison examples set forth above, the production ofmetal nanoparticles with alkanoate molecules as capping molecules takesa long time and requires several procedures, so that the process iscomplicated and the amount of metal nanoparticles retrieved is little.

REFERENCE EXAMPLE

5 g of AgNO₃ was dissociated in 30 g of propylamine. The color of thesolution was transparent or a faint yellow. With the addition of 4.2 gof dodecanethiol, white sediments were formed. The sediments wereinsoluble not only in a hydrophilic solvent such as water and alcohol,but also in hydrophobic solvents such as toluene. The dried whitesediments were analyzed via WAXS (wide-angle X-ray scattering), DSC(differential scanning calorimetry) and TGA (thermo-gravimetricanalysis). The analysis results of DSC revealed that the melting pointwas 133° C., and the results of WAXS revealed that they had a lamellarstructure. Also, the results of TGA revealed that silver ions anddodecanethiol underwent a 1:1 reaction. Therefore, it is found that thewhite sediments formed is silver thiolate (C₁₂H₂₅S—Ag).

FIG. 9 is a graph representing the results of WAXS (wide-angle X-rayscattering) analysis of silver thiolate for producing metalnanoparticles according to an embodiment of the invention. FIG. 9 is agraph representing the analysis results of WAXS for the white sedimentsobtained in the Reference Example set forth above.

EXAMPLE 9

5 g of AgNO₃ was dissociated in 20 g of propylamine. The color of thesolution was transparent or a faint yellow. The mixture was stirredafter adding 50 g of xylene, and then 4.2 g of dodecanethiol was added,at which white sediments were formed. The temperature was raised to theboiling point of xylene, and at 130° C. and higher, the white sedimentsstarted to disappear. The solution was yellow, and turned red afterabout 1 hour of the reaction, to consequently turn into a thick browncolor. The total reaction time was about 4 hours, and after addingethanol to the thick brown solution and precipitating, the particleswere collected by centrifugal separation. The results of analyzing theparticles with a UV-VIS spectroscope are the same as those in FIG. 1,and the TEM image is the same as that in FIG. 2. These analyses revealthat ultimately, silver nanoparticles having a uniform size of 5 nm wereformed.

EXAMPLE 10

1-hexadecene was used instead of xylene as the reflux medium of Example9. Ultimately, it was found that silver nanoparticles having a uniformsize of 5 nm were formed.

EXAMPLE 11

5 g of AgNO₃ was dissociated in 20 g of propylamine. The color of thesolution was transparent or a faint yellow. The mixture was stirredafter adding 50 g of xylene, and then 8.4 g of dodecanethiol was added,at which white sediments were formed. The temperature was raised to theboiling point of xylene, and at 130° C. and higher, the white sedimentsstarted to disappear. The solution was yellow, and turned red afterabout 1 hour of the reaction, to consequently turn into a thick browncolor. The total reaction time was about 4 hours, and after addingethanol to the thick brown solution and precipitating, the particleswere collected by centrifugal separation. Ultimately, it was found thatsilver nanoparticles having a uniform size of 5 nm were formed.

EXAMPLE 12

1-hexadecene was used instead of xylene as the reflux medium of Example11, and it was found that, ultimately, silver nanoparticles having auniform size of 5 nm were formed.

EXAMPLE 13

5 g of AgNO₃ was dissociated in 20 g of propylamine. The color of thesolution was transparent or a faint yellow. The mixture was stirredafter adding 50 g of n-hexane, and then 4.2 g of dodecanethiol wasadded, at which white sediments were formed. The temperature was raisedto the boiling point of n-hexane, and as soon as 1 g of TBAB was added,the solution turned into a red color, and ultimately into a thick browncolor. After the completion of the reaction, it was found that silvernanoparticles having a uniform size of 5 nm were formed.

EXAMPLE 14

Toluene was used instead of n-hexane as the reflux medium of Example 13,and it was found that, at the completion of the reaction, silvernanoparticles having a uniform size of 5 nm were formed.

EXAMPLE 15

Xylene was used instead of n-hexane as the reflux medium of Example 13,and it was found that, at the completion of the reaction, silvernanoparticles having a uniform size of 5 nm were formed.

EXAMPLE 16

1-hexadecene was used instead of n-hexane as the reflux medium ofExample 13, and it was found that, at the completion of the reaction,silver nanoparticles having a uniform size of 5 nm were formed.

EXAMPLE 17

5 g of AgNO₃ was dissociated in 20 g of propylamine. The color of thesolution was transparent or a faint yellow. The mixture was stirredafter adding 50 g of xylene, and then 8.4 g of dodecanethiol was added,at which white sediments were formed. The temperature was raised to theboiling point of xylene, and at 130° C. and higher, the white sedimentsstarted to disappear. As soon as 1 g of TBAB was added, the solutionturned into a red color, and ultimately into a thick brown color. Afterthe completion of the reaction, it was found that silver nanoparticleshaving a uniform size of 5 nm were formed.

EXAMPLE 18

1-hexadecene was used instead of xylene as the reflux medium of Example17, and it was found that, at the completion of the reaction, silvernanoparticles having a uniform size of 5 nm were formed.

COMPARISONS 3, 4, 5

In Comparison 3, 5 g of AgNO₃ was dissociated in 20 g of propylamine.The color of the solution was transparent or a faint yellow. The mixturewas stirred after adding 50 g of n-hexane, and then 16.8 g ofdodecanethiol was added, at which white sediments were formed. Thetemperature was raised to the boiling point of n-hexane, for a reactiontime of 8 hours. As a result, the white sediments were not dissolved,and hence silver nanoparticles were not formed.

In Comparison 4, toluene was used instead of n-hexane as the refluxmedium of Comparison 3, and in Comparison 5, xylene was used instead ofn-hexane. Similarly, the white sediments were not dissolved, and hencesilver nanoparticles were not formed.

Here, it is found that silver nanoparticles are not formed whendodecanethiol is added in a mole ratio of 2 with respect to AgNO₃.

COMPARISONS 6, 7, 8

In Comparison 6, 5 g of AgNO₃ was dissociated in 20 g of propylamine.The color of the solution was transparent or a faint yellow. The mixturewas stirred after adding 50 g of n-hexane, and then 16.8 g ofdodecanethiol was added, at which white sediments were formed. Thetemperature was raised to the boiling point of n-hexane, and 1 g of TBABwas added. As a result, the white sediments were not dissolved, andhence silver nanoparticles were not formed.

In Comparison 7, toluene was used instead of n-hexane as the refluxmedium, and in Comparison 8, xylene was used instead of n-hexane. As aresult, the white sediments were not dissolved, and hence silvernanoparticles were not formed. Here, it is found that silvernanoparticles are not formed when dodecanethiol is added in a mole ratioof 2 with respect to AgNO₃, even when a reducing agent of TBAB is added.

Production of Conductive Ink

100 g of silver nanoparticles 5 nm in size, produced by Examples 9through 18, were placed in an aqueous diethylene glycol butyl etheracetate and ethanol solution, and dispersed with an ultra-sonicator toproduce 20 cps of conductive ink. The conductive ink thus produced maybe printed on a circuit board via inkjet techniques to form conductivewiring.

While the embodiments of the present invention have been described withreference to methods of producing silver nanoparticles, it is apparentthat the methods may be applied equally to metal compounds includingmetals mentioned above besides silver salt, to produce metalnanoparticles in a manner described in one of the embodiments.

The present invention provides a method of producing metal nanoparticlesusing a hydrophobic solvent, having uniform particle size distributionand high yield rate to allow mass production. Also, the presentinvention provides metal nanoparticles having alkanoate molecules orsulfur molecules, produced at a low cost by an integrated procedure, andprovides conductive ink including the metal nanoparticles thus obtained.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the present invention, the scope of which isdefined in the appended claims and their equivalents.

1. A method of producing metal nanoparticles, said method comprising:dissociating a metal compound with an amine-based compound; and adding ahydrocarbon-based compound and either one of an alkanoic acid or athiol-based compound to the dissociated metal ion solution.
 2. Themethod of claim 1, wherein the metal compound includes one or moremetals selected from a group consisting of silver (Ag), copper (Cu),nickel (Ni), gold (Au), platinum (Pt), palladium (Pd), and iron (Fe). 3.The method of claim 2, wherein the metal compound includes one or morecompounds selected from a group consisting of AgNO₃, AgBF₄, AgPF₆, Ag₂O,CH₃COOAg, AgCF₃SO₃, and AgClO₄.
 4. The method of claim 1, wherein theamine-based compound has a composition of C_(x)H_(2x+1)NH₂, where x isan integer from 2 to
 20. 5. The method of claim 4, wherein theamine-based compound is one or more compounds selected from a groupconsisting of butylamine, propylamine, octylamine, decylamine,dodecylamine, hexadecylamine, and oleylamine.
 6. The method of claim 1,wherein the mole ratio of the amine-based compound to the metal compoundranges from 1 to
 100. 7. The method of claim 1, wherein thehydrocarbon-based compound is one or more compounds selected from agroup consisting of hexane, octane, decane, tetradecane, hexadecane,1-hexadecene, 1-octadecene, toluene, xylene, and chlorobenzoic acid. 8.The method of claim 1, wherein the hydrocarbon-based compound is addedso that the concentration of the metal compound becomes a mole ratio of0.001 to
 10. 9. The method of claim 1, wherein the alkanoic acid has acomposition of RCOOH, where R is a saturated or unsaturated aliphatichydrocarbon from C₁ to C₂₀.
 10. The method of claim 9, wherein thealkanoic acid is one or more acids selected from a group consisting oflauric acid, oleic acid, decanoic acid, and palmitic acid.
 11. Themethod of claim 1, wherein the mole ratio of the alkanoic acid to themetal compound ranges from 0.1 to
 1. 12. The method of claim 1, whereinthe thiol-based compound has a composition of C_(y)H_(2y+1)SH, where yis an integer from 2 to
 20. 13. The method of claim 12, wherein thethiol-based compound is one or compounds selected from a groupconsisting of linear-structure octanethiol, decanethiol, dodecanethiol,tetradecanethiol, hexadecanethiol, octadecanethiol andbranched-structure 2-methyl-2-propanethiol.
 14. The method of claim 1,wherein the mole ratio of the thiol-based compound to the metal compoundranges from 0.1 to
 1. 15. The method of claim 1, wherein a reducingagent is further added during the adding of a hydrocarbon-based compoundand either one of an alkanoic acid or a thiol-based compound to thedissociated metal ion solution.
 16. The method of claim 15, wherein thereducing agent is one or more compounds selected from a group consistingof boron hydroxide, hydrazine, alcohol, amide, acid, and glucose. 17.The method of claim 15, wherein the reducing agent is one or morecompounds selected from a group consisting of NaBH₄, LiBH₄,tetrabutylammonium borohydride, N₂H₄, glycol, glycerol,dimethylformamide, tannic acid, citrate, and glucose.
 18. The method ofclaim 15, wherein the mole ratio of the reducing agent to the metalcompound ranges from 0.1 to
 1. 19. Metal nanoparticles, produced by amethod comprising: dissociating a metal compound with an amine-basedcompound; and adding a hydrocarbon-based compound and an alkanoic acidto the dissociated metal ion solution.
 20. The metal nanoparticles ofclaim 19, wherein the size of the metal nanoparticles is 1 to 40 nm. 21.The metal nanoparticles of claim 19, including 10 to 40 weight % organiccomponents among the metal nanoparticles.
 22. The metal nanoparticles ofclaim 19, used an antibiotic, a deodorant, a disinfectant, a conductiveadhesive, a conductive ink, or an electromagnetic shield for a displaydevice.
 23. Metal nanoparticles, produced by a method comprising:dissociating a metal compound with an amine-based compound; and adding ahydrocarbon-based compound and a thiol-based compound to the dissociatedmetal ion solution.
 24. The metal nanoparticles of claim 23, wherein thesize of the metal nanoparticles is 1 to 20 nm.
 25. The metalnanoparticles of claim 23, having 1 to 6 weight % of sulfur.
 26. Themetal nanoparticles of claim 23, used an antibiotic, a deodorant, adisinfectant, conductive adhesive, conductive ink, or an electromagneticshield for a display device.
 27. Conductive ink including metalnanoparticles produced by a method comprising: dissociating a metalcompound with an amine-based compound; and adding a hydrocarbon-basedcompound and either one of an alkanoic acid or a thiol-based compound tothe dissociated metal ion solution.